:root {
  --bg-main: #0b0f19;
  --bg-panel: #0f1629;
  --bg-key: #1a2140;
  --bg-key-hover: #222b55;
  --bg-accent: #2563eb;
  --bg-equals: #22c55e;

  --text-primary: #e5e7eb;
  --text-secondary: #94a3b8;
  --text-accent: #38bdf8;

  --radius-lg: 16px;
  --radius-md: 12px;
  --radius-sm: 8px;
}

* {
  box-sizing: border-box;
  font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
}

body {
  margin: 0;
  height: 100vh;
  background: radial-gradient(1200px circle at top, #292323 0%, #222636 40%, #000414 100%);
  display: flex;
  align-items: center;
  justify-content: center;
}

/* ---------------- CONTAINER ---------------- */

.calculator {
  width: 360px;
  background: linear-gradient(180deg, #0f172a, #020617);
  border-radius: var(--radius-lg);
  padding: 20px;
  box-shadow:
    0 20px 40px rgba(0, 0, 0, 0.7),
    inset 0 1px 0 rgba(255, 255, 255, 0.03);
}

/* ---------------- DISPLAY ---------------- */

.display {
  background: linear-gradient(180deg, #020617, #020617);
  border-radius: var(--radius-md);
  padding: 16px;
  margin-bottom: 14px;
  text-align: right;
  border: 1px solid rgba(255, 255, 255, 0.04);
}

#expression {
  font-size: 14px;
  color: var(--text-secondary);
  min-height: 18px;
  letter-spacing: 0.3px;
}

#result {
  font-size: 34px;
  font-weight: 600;
  color: var(--text-accent);
  margin-top: 4px;
}

/* ---------------- TOP BAR ---------------- */

.top {
  display: flex;
  justify-content: space-between;
  margin-bottom: 12px;
}

.top button {
  background: var(--bg-key);
  color: var(--text-primary);
  border: 1px solid rgba(255, 255, 255, 0.05);
  padding: 6px 14px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 13px;
}

.top button:hover {
  background: var(--bg-key-hover);
}

/* ---------------- KEYS GRID ---------------- */

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

/* ---------------- BUTTONS ---------------- */

button {
  height: 48px;
  background: linear-gradient(180deg, var(--bg-key), #141b36);
  color: var(--text-primary);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: var(--radius-md);
  font-size: 16px;
  cursor: pointer;
  transition: all 0.12s ease;
}

button:hover {
  background: linear-gradient(180deg, var(--bg-key-hover), #1c2450);
}

button:active {
  transform: translateY(1px);
}

/* ---------------- SPECIAL KEYS ---------------- */

[data-op] {
  color: #c7d2fe;
}

[data-fn] {
  color: #a5b4fc;
  font-size: 15px;
}

#equals {
  background: linear-gradient(180deg, var(--bg-equals), #16a34a);
  color: #022c22;
  font-weight: 600;
  border: none;
}

#equals:hover {
  filter: brightness(1.05);
}

/* ---------------- ACCESSIBILITY ---------------- */

button:focus-visible {
  outline: 2px solid var(--bg-accent);
  outline-offset: 2px;
}